Razor Blade Technology

ABSTRACT

A razor cartridge includes razor blade assemblies having an inter-blade guard attached to a side of a razor blade. The razor blade is formed from strip that is manufactured including a thermal oxidation process to form a chromium oxide layer on the side surface of the razor blade. This oxide film prevents electrochemical corrosion of the razor blade that may be visible to a user and prevents real or perceived premature failure of the razor blade and thus the razor cartridge during its extended life. The razor blade assembly may also have an array of closely spaced droplets of a liquid adapted to inhibit corrosion of the razor blade applied to the side of the razor blade visible to a user.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/349,706, filed Jan. 13, 2012 which claims the benefit ofInternational Application PCT/US2010/041,964, filed Jul. 14, 2010 whichclaims the benefit of U.S. provisional patent application Ser. No.61/225,586, filed Jul. 15, 2009, the contents of which are incorporatedherein for reference in their entireties.

BACKGROUND

1. Technical Field

The present disclosure relates to razor blades for razor cartridges ingeneral and, more particularly, to a method of manufacturing a razorblade.

2. Background

Many modern safety razors include a disposable razor cartridge adaptedto be selectively connected to a reusable handle by connecting structuretherebetween. The cartridge includes a housing having at least one razorblade with a cutting edge disposed therein. Other modern safety razorsinclude a razor cartridge permanently connected to the handle that canbe disposed of as a single unit.

In commonly assigned U.S. patent application Ser. No. 11/150,744,published as US 2006/0277759, now U.S. Pat. No. 7,681,314, thedesirability of providing a razor blade assembly including aninter-blade guard joined to a razor blade is disclosed. The provision ofan inter-blade guard permits adjacent cutting edges to be spacedsufficiently far apart in their razor cartridge to allow adequaterinsing of debris from the space between adjacent blades and anyrespective support structure while the inter-blade guard provides a skinengaging/skin supporting surface between adjacent cutting edges tocontrol skin bulge and provide improved shaving comfort and reduction ofnicks and cuts. The inter-blade guard is mounted on the razor blade in aposition generally visible to a user during normal use and handling ofthe safety razor.

A razor cartridge including a razor blade having a bent portion can havecertain advantages and there have been many proposals to provide a razorcartridge with such a razor blade. However, such razor cartridges havenot been successfully commercialized or at least not manufactured on ascale that is significant in a mass market such as that of razorcartridges. Many manufacturers emulate a bent razor blade by mounting agenerally planar razor blade on a bent support made from a material boththicker and softer than a typical hardened razor blade. U.S. Pat. No.4,586,255 to Jacobson discloses a typical construction of a blademounted on a support. The support is mounted on the opposed side of therazor blade to the blade guard of the aforementioned U.S. Pat. No.7,681,314 patent the razor blade and is at least partially hidden fromview by a user during normal use and handling of the safety razor.

Modern safety razors are normally used and can be stored by a user in amore or less wet or humid environment. In normal use, the razor bladesof a razor cartridge are brought into contact with mildly corrosivesubstances, such as the constituents of sweat, soap, and shaving aidssuch as shaving foam or gel. Also the nature and composition of tapwater (which is generally used for shaving) can vary from city to city.In view of these ambient conditions, martensitic stainless steels havebecome widely used as a corrosion-resisting material for making razorblades having a high level of cutting quality.

The inter-blade guard on the other hand is preferably manufactured froma fully annealed low-carbon stainless steel such as grade AISI 301/DIN1.4310. This material is chosen for several reasons including ease offorming its desired profile, such as those disclosed in theaforementioned U.S. Pat. No. 7,681,314 patent. For convenience ofassembly, the inter-blade guard can be joined by welding, e.g. laserspot welding, to its respective razor blade.

Small compositional differences can thus exist between the razor bladeand its inter-blade guard assembled thereto. In use, moisture and otherconstituents can be trapped and retained between the razor blade and itsinter-blade guard. This can act as an electrolyte and thus the razorblade, inter-blade guard and moisture therebetween can comprise anelectrochemical cell that can result in localized electrochemicalcorrosion of the razor blade. As the inter-blade guard is mounted on therazor blade in a position visible to a user any such corrosion can alsobe visible to a user and can be at least considered unsightly and maycause real or perceived premature failure of the razor blade and thusrazor cartridge having such a razor blade assembly. Moreover, manymodern safety razor cartridges can have an extended useful life comparedto earlier razor cartridges. Improved coatings on cutting edges (e.g.hard carbon) can increase the useful life of the cutting edge andimprovements in the composition or construction of so-called lubricatingstrips can extend the life of the lubricating strip. A modern safetyrazor cartridge having an extended life has more opportunity to suffercorrosion during its life than an earlier razor cartridge.

SUMMARY

The present disclosure has for its objective to eliminate, or at leastsubstantially alleviate the limitations of the prior art razor bladeassemblies. The present disclosure in one aspect is directed to a methodof manufacturing a razor blade assembly for a razor cartridge,comprising the steps of providing an elongated strip of stainless steelof a first composition, the strip including a front edge and a firstside, processing the strip to effect a martenstic transformation toharden the strip, and providing a cutting edge extending along the frontedge of the elongated strip. The strip is cut into lengthwise extendingportions to provide discrete razor blades having a length suitable foruse in a razor cartridge housing. A chromium oxide layer is formed onthe first side of the razor blade by a thermal oxidation process. Aninter-blade guard is permanently joined to the first side of the razorblade. The razor blade and the inter-blade guard comprise stainlesssteels of different compositions and the layer of chromium oxideprevents or delays the onset of user-visible electrochemical corrosionof the first side of the razor blade. The razor blade assembly isassembled to a housing to provide a razor cartridge. A predeterminedarray of closely spaced droplets of a liquid adapted to inhibitcorrosion of the razor blade can be applied to a portion of the firstside of the razor blade; a portion of a skin engaging surface of theinter-blade guard and can penetrate a gap between the first side and theinter-blade guard to further prevent or delay the onset of user-visibleelectrochemical corrosion of the first side of the razor blade. Theapplication of the array of droplets a liquid adapted to inhibitcorrosion of the razor blade is preferably performed to the assembledrazor cartridge. The droplet array is preferably restricted to the razorblade assembly and suitably controlled so that the aforementioned liquidis not unnecessarily applied to e.g. outer surfaces of the housing.

These and other advantages of the present disclosure will be apparent toone of ordinary skill in the art in light of the following DetailedDescription and Drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an embodiment of a razor blade and aninter-blade guard.

FIG. 2 is a schematic view of an embodiment of process equipment toprovide a chromium oxide layer.

FIG. 3 is a schematic cross section of a razor cartridge including arazor blade and inter-blade guard.

FIG. 4 is a schematic plan view of apparatus to deposit a liquidcorrosion inhibitor to a razor cartridge.

FIG. 5 is a schematic plan view of the razor cartridge of FIG. 3 afterprocessing in the apparatus of FIG. 4.

DETAILED DESCRIPTION

Referring now to the drawings, and in particular FIG. 1, a sectionalview of a razor blade assembly 10 for use in a razor cartridge (100 inFIG. 3) is depicted. A razor blade 20 includes a stainless steelsubstrate, which typically has a thickness of about 0.05-0.10 mm. Thestainless steel typically contains about 0.4 to 0.7% carbon and about 12to 13.5% chromium, both by weight. The stainless steel has been hardenedto effect a martensitic transformation to harden the substrate materialto e.g. 700-850 HV. In the present disclosure, HV designates hardnessmeasured on the Vickers scale at a 1.0 kg load. The blade 20 has acutting edge 22 and a body 24 having a first side and a second side, 26,28 respectively. An inter-blade guard 30 is attached to the first side26 of the razor blade 20. The inter-blade guard includes a surface 36adapted to contact a skin surface of a user during a normal use of therazor cartridge. Further desired features and function of theinter-blade guard are disclosed in the aforementioned U.S. Pat. No.7,681,314, incorporated herein for reference in its entirety.

The inter-blade guard 30 is preferably manufactured from an annealedlow-carbon austenitic stainless steel such as grade AISI 301 (DIN1.4310) and has a thickness preferably in the range about 0.05-0.076 mmalthough the present disclosure is not limited in this regard and othermaterials that may be readily formed to a desired profile and/or joinedto the razor blade may be usefully employed. The inter-blade guard 30 ispermanently joined to the razor blade for example by a known laser spotwelding process (FIG. 1 sectionally depicts the welding zone 32). Otherjoining methods may also be employed such as use of a suitable adhesivesuch as an epoxy (e.g. a two-part epoxy) or cyanoacrylate.

The razor blade assembly 10 can also comprise a support member 40 as iswell known in the art.

The razor blade 20 is manufactured as follows. First, a rolled sheet ofstainless steel is slit into elongated strips. The strips can beperforated for ease of handling during subsequent processing. Otherpre-hardening steps, such as scoring, may be performed, if desired.

When the desired sequence of pre-hardening steps has been completed, thestrip is subjected to a hardening process, which includesaustenitization of the stainless steel. The hardening process isconducted in a first muffle furnace or tunnel oven. The strip isprovided in coil form and is uncoiled and fed into the furnace where itis quickly ramped up to a high temperature, e.g., approximately 1160°C., maintained at this temperature for a period of time, during whichaustenization of the stainless steel occurs. The strip is then rapidlyquenched (e.g. in an ice-box) to a low temperature e.g. approximately−70° C., to effect a martensitic transformation of the stainless steelsubstrate material. The strip is recoiled and passes to subsequentprocesses. The hardness of the strip thus processed has a hardnessapproximately 700-850 HV.

The strip is subsequently sharpened by known process steps to provide acutting edge. After the process to provide a cutting edge the strip canbe severed into lengthwise extending portions to provide razor bladeshaving a length suitable for use in a razor cartridge and stacked oneupon the other in suitable carriers or the strip can be recoiled forfurther processing. If necessary, the stack of razor blades (or recoiledstrip) is then cleaned by any one of a number of processes known in theart to remove residues from the sharpening process and othercontamination. Coatings are applied to the cutting edge that can bemetallic (e.g. titanium, niobium or chromium), ceramic (e.g. chromiumnitride) or hard carbon (e.g. amorphous diamond or DLC (diamond-likecarbon) or combinations thereof and a further outer layer of a lowfriction coating of a fluorinated polymer such as PTFE is applied. ThePTFE is applied by spraying a suspension of PTFE particles in a suitablemedium such as water and/or alcohol on to the cutting edge(s). To effecta continuous adherent (i.e. cured) film of PTFE, the razor blades intheir carrier or the strip in its coil are loaded on a conveyor andpassed through a second muffle furnace or tunnel oven at approx 360° C.to cure the PTFE. Reheating the razor blades to perform the PTFE curingprocess has the effect of partially annealing the razor blades to ahardness about 600 HV or more, e.g. about 680 HV. The process equipmentis schematically shown in FIG. 2 which depicts stacked blades incarriers 48 that are transported on conveyor 50 though furnace 60.

As previously mentioned, modern safety razors are normally used in a wetenvironment and can be stored by a user in a variably humid environment.When used, the razor blades of a razor cartridge are brought intocontact with a variety of mildly corrosive substances in a variety ofconcentrations, such as the constituents of sweat, soap, and shavingaids such as shaving foam or gel. Furthermore, the composition oftypical tap water as is generally used for shaving can vary from city tocity. Moreover, modern safety razor cartridges can have an extendeduseful life compared to earlier razor cartridges. Improved coatings oncutting edges (e.g. hard carbon) can increase the useful life of thecutting edge and improvements in the composition or construction ofso-called lubricating strips can extend the life of the lubricatingstrip of the razor cartridge. A modern safety razor cartridge having anextended life has more opportunity to suffer corrosion during its lifethan an earlier razor cartridge.

To enhance corrosion resistance of the stainless steel material of therazor blade over a range of possible use environments a chromium oxidelayer is formed on outer sides (26, 28) by a thermal oxidation process.The razor blade is introduced into an atmosphere of clean dry air atapproximately 160° C. to 215° C., e.g. 190° C. In simplified terms, theaforementioned hardening process converts a portion of the chromium andcarbon of the stainless steel material to chromium carbide whichpartially provides the cited hardness. Some chromium remains unreactedwith carbon and this so-called free chromium at the surface of thestainless steel is oxidized as follows to form a corrosion resistingchromium oxide layer on the stainless steel substrate.

The razor blades in their carrier are passed through a third mufflefurnace or tunnel oven 70 that is preferably arranged sequentially withthe second furnace 60 to advantageously benefit from the provision ofthe conveyor 50 for the PTFE curing process. The furnace is set to theaforementioned temperature 160° C. to 215° C., e.g. 190° C. and cleandry air 80 at ambient temperature is passed through the furnace muffletube 82 in the direction indicated or in the reverse direction. Theaforementioned temperature range is selected to avoid any significantfurther partial annealing of the razor blades. A chromium oxide layer isformed on the outer sides of the razor blades.

The thickness of the chromium oxide layer is preferably controlled toabout 10 nm to about 15 nm thick (about 100 Å to about 150 Å). Athickness less than about 10 nm is less preferred as the razor blade canlack a desired increase in corrosion resistance. A thickness more thanabout 15 nm is less preferred as the corrosion resistance of the razorblade is not proportionately increased. Also a thickness of more thanabout 15 nm can result in an undesirable color change of the surface ofthe razor blade that can be subjectively recognized by a casualobserver. Preferably the thickness of the chromium oxide layer does notsubstantially alter the color of the razor blade as a color change canbe deemed commercially undesirable for a razor blade or a razorcartridge including such a razor blade. Control of the thickness of thechromium oxide layer can be controlled by primarily adjusting the timethe strip is in the furnace (e.g. by adjusting the conveyor speed)and/or the temperature of the furnace and secondarily by adjusting theair flow rate through the muffle tube of the furnace.

In other embodiments the third furnace can be arranged separately fromthe second furnace. The third furnace can also be arranged sequentiallywith the first furnace and ice-box in which case the oxide layer isformed on the strip before the provision of the cutting edge andsubsequent coatings. As an alternative to use of a muffle furnace thethird furnace can also be a sealed furnace and blade carriers or entirecoils of strip can be processed therein in a so-called batch process.

It is known to provide a chromium oxide layer up to about 8 nm (80 Å)thick by chemical or electrochemical passivation. However, this processis undesirable in present-day manufacturing for various reasonsincluding: capital cost; the environmental impact of use and subsequentdisposal of the chemicals required and general storage, health andsafety issues.

Corrosion resistance of strip or of a razor blade made from the strip ora razor cartridge including such a razor blade is assessed in anaccelerated corrosion test as follows:

-   -   a) A test specimen that can be include a portion of strip or a        razor blade made from the strip or a razor cartridge including        such a razor blade is dipped in a 0.2% salt solution at 60° C.        for 10 seconds.    -   b) The specimen is removed from the solution and placed in a        Temperature/Humidity oven at 60° C., 95% RH (relative humidity)        for 25 minutes.    -   c) The specimen is removed from the oven and visually inspected        at up to 2.5× magnification and any corrosion is compared to a        predefined severity rating scale.    -   d) Steps a) to c) are repeated for a total of 15 cycles.

Referring back to FIG. 1, the razor blade can be joined to a metallicsupport 40 as is well known in the art, e.g. as disclosed in U.S. Pat.No. 4,586,255 to Jacobson. An inter-blade guard 30 (as previouslydescribed) is joined to a side of the razor blade, the side beingvisible to a user during normal use and handling of the safety razorincluding such a razor blade. As can be seen in FIG. 1 certain narrowgaps 34 exist between the razor blade and the inter-blade guard that cantrap moisture and/or a dilute mildly corrosive substance after use andretain said moisture etc by capillary/surface tension effects. Aspreviously mentioned, the composition of the stainless steels of therazor blade and the inter-blade guard can be slightly different. Withoutthe protective chromium oxide layer on the razor blade acting as aninsulator an electrochemical cell could be created of an anode andcathode being the razor blade and inter-blade guard and an electrolytebeing the moisture etc. thus resulting in electrochemical corrosion thatwill occur on the razor blade on a side visible to a user and that couldbe sufficient to be undesirably visible to the user.

Referring now to FIG. 3 an exemplary schematic cross section of a razorcartridge 100 including a razor blade and inter-blade guard assembly 10is depicted. The razor cartridge can be generally as disclosed in theaforementioned '255 patent or can be another type of razor cartridge andthe present disclosure is not limited to the type of razor cartridge.The razor cartridge can also include more than two razor bladeassemblies 10, e.g. three, four or more and the present disclosure isnot limited to the number of razor blade assemblies 10 in the razorcartridge. The cartridge includes a housing 110 that comprises a guard112, a cap 114 and a blade mounting region 116. A (vertical) portion ofthe blade support 40 is disposed in slots 126 of the end wall 118 of thehousing 110 to provide independent movement of each blade assembly underthe forces encountered during shaving. The guard and the cap cancomprise, respectively, elastomeric and lubricious elements 122, 124, asare well known in the art. A spring element 130 can be provided as iswell known in the art.

Referring now to FIG. 4, apparatus for a further advantageous process toinhibit corrosion of a razor blade assembly of a razor cartridge isschematically depicted in plan view. This process can be performed inaddition to, or in the alternative to the thermal oxidation processpreviously described. After assembly of a razor cartridge, e.g. a razorcartridge as depicted in FIG. 3, the razor cartridge 100 is placed on aconveyor 150, preferably in a nest 152 of a conveyor, preferably anindexing conveyor. The razor cartridge is positioned so that the cuttingedges and inter-blade guards of the blade assemblies are exposed. Duringthe indexing dwell at position 154 spray head 160 passes over thecartridge preferably in a direction transverse to the direction ofmotion of the conveyor. The spray head 160 has a controlled spraypattern to deposit a predetermined closely packed array (170 in FIG. 5)of droplets of a liquid rust inhibitor/oil mix on the exposed surfacesof the blade assemblies of the razor cartridge. Preferably the spraypattern is restricted to the aforementioned surfaces of the bladeassemblies and is not unnecessarily applied to e.g. outer surfaces ofthe housing. In order to achieve suitable control of the spray patternpreferably the spray head is an ink jet spray head modified to spray apredetermined array of rust inhibitor/oil mix in place of ink A suitableink jet spray head is a SCANTRUE II provided by TRIDENT. Modification ofthe spray head to be suitable for the aforementioned mix includesreplacing the internal seals (e.g. “O” rings) with seals of VITONmaterial to resist deterioration from contact with the aforementionedmix. The rust inhibitor/oil mix is also formulated to have a viscosityapproximately equivalent to typical inks used in such ink jet equipment,e.g. about 7-10 centistokes and preferably comprises (each by volume)10% rust inhibitor such as CRODASINIC-O and/or CRODAZOLINE-O bothprovided by CRODA INC and more preferably comprises 5% of each rustinhibitor. The mixture further preferably comprises 70% mineral oil suchas Naphtha Hydrotreated Heavy oil provided by EXXON MOBIL. The mixturefurther preferably comprises 20% mineral spirits, e.g. odourless mineralspirits. The rust inhibitor/oil mix preferably avoids separation to itsconstituent parts over an extended period, e.g. 25 days or more. Therust inhibitor/oil mix also preferably has a surface tension low enoughto resist beading on the exposed surfaces of the blade assemblies of therazor cartridge. The spray pattern of the spray head can be programmedby conventional ink jet spray control equipment to spray a closelypacked array of droplets as previously mentioned. The spray head can bearranged to pass over each razor cartridge once, twice (i.e. by aforward and back motion synchronized to each index of the conveyor) ormore times depending on the desired deposition quantity of the mix. Asthe spray head is programmable razor cartridges having various exposedblade arrangements can be accommodated, e.g. the exposed arrangement canbe rectangular, trapezoidal, oval etc. The total quantity of rustinhibitor/oil mix thus applied can be about 2 mg per razor cartridge. Asthe rust inhibitor/oil mix is a liquid, some liquid thus applied willflow at least partially into the gap 34 between the razor blade and theinter-blade guard by capillary action. This can delay or prevent theaforementioned ingress of moisture and/or a dilute mildly corrosivesubstance into the gap and in turn delay or prevent the onset ofuser-visible electrochemical corrosion. Also as the rust inhibitor/oilmix remains liquid and resists beading, over a short time the dropletswill spread and eventually merge with adjacent droplets to provide asubstantially continuous film over the applied surfaces. In anaccelerated corrosion test as previously described, a razor cartridgetreated by this apparatus can have threshold for unacceptable corrosiongreater than 2-3 times that of an untreated razor cartridge.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. For instance, modifications or changes as can be made withinthe scope of the attached claims and features disclosed in connectionwith any one embodiment can be used alone or in combination with eachfeature of the respective other embodiments. Thus, the breadth and scopeof any embodiment should not be limited by any of the above describedexemplary embodiments, but should be defined only in accordance with thefollowing claims and their equivalents.

What is claimed is:
 1. A method of making a razor blade assembly for arazor cartridge, comprising the steps of: a) providing a razor bladecomprising a stainless steel of a first composition, the razor bladehaving a first side and a cutting edge extending along a front edgethereof, the razor blade further having been processed to effect amartensitic transformation thereof to harden the razor blade; b)providing a chromium oxide layer on the first side by a thermaloxidation process of free chromium, defined as chromium of the stainlesssteel unreacted with carbon of the stainless steel, at the surface ofthe stainless steel to enhance corrosion resistance; and c) permanentlyjoining an inter-blade guard to the first side of the razor blade, theinter-blade guard comprising a stainless steel of a second compositionand including a surface adapted to contact a skin surface of a userduring a normal use of the razor cartridge including the razor bladeassembly.
 2. The method of claim 1, further comprising the step ofapplying to at least a portion of the first side of the razor blade anarray of closely spaced droplets of a liquid adapted to inhibitcorrosion of the razor blade.
 3. The method of claim 1, furthercomprising the step of assembling the razor blade assembly to a housing,the resultant assembly comprising the razor cartridge; and wherein thestep of applying the array of closely spaced droplets of a liquidadapted to inhibit corrosion of the razor blade occurs after the razorblade is assembled to the housing.
 4. The method of claim 1, wherein thechromium oxide layer is between about 10 nm and 15 nm thick, and whereinthe chromium oxide layer does not substantially alter a color of thefirst side of the razor blade.
 5. A method of making a razor bladeassembly for a razor cartridge, comprising the steps of: a) providing arazor blade comprising a stainless steel of a first composition, therazor blade having a first side and a cutting edge extending along afront edge thereof; b) permanently joining an inter-blade guard to thefirst side of the razor blade, the inter-blade guard comprising astainless steel of a second composition and including a surface adaptedto contact a skin surface of a user during a normal use of the razorcartridge including the razor blade assembly; and c) applying to atleast a portion of the first side of the razor blade an array of closelyspaced droplets of a liquid adapted to inhibit corrosion of the razorblade.